Immersion heater



June 12, 1951 sMlTH 2,556,984

IMMERSION HEATER Filed Feb. 14, 1946 INVEN TOR. FRANK E. SMITH AGENTPatented June 12, 1951 i IMIWERSION HEATER Frank E. Smith, NiagaraFalls, N. Y., assignor to E. I. du Pont de Nemours & Company,Wilmington, Del., a corporation of Delaware Application February 14,1946, Serial No. 647,522

2 Claims.

This invention relates to gas or oil heaters particularly heaters of theimmersion type adapted to be partially immersed in liquid to be heated.

Immersion heaters are known which are constructed in the form of a U orhairpin. Gas or oil with suflicient air is delivered to the end of oneleg of the U so that combustion occurs as the gaseous products travelthrough the U and out of the second leg to a stack. The heater isemployed by immersing the lower part of the U into the liquid to beheated with the legs extending above the liquid. When used for heatingliquids at high temperatures, e. g. fused salt mixtures at temperaturesaround 800900 C., delivery of heat is generally inadequate especiallywhen the liquid being heated is employed as a reaction medium forcarrying out a chemical reaction requiring a large heat input. Attemptshave been made to increase the heating capacity by delivering fuelpremixed with sufficient air to support complete combustion to the lowerpart of the U. Such a practice, while successful in supplying largeamounts of heat due to the almost instantaneous type of combustionresulting from igniting fuel premixed with air, rapidly burns out theheater in the vicinity of the bend of the U. If fuel and air aresupplied separately to the bend of the U, the maximum heat obtainablefrom the fuel is not developed before the gases escape to the stack.

It is an object of my invention to provide an immersion type heater ofsuch construction that those parts thereof which are immersed in theliquid to be heated will be the parts in which maximum evolution of heatis attained. A further object is to provide an immersion type heatercapable of supplying to the liquid being heated a large amount of heatat high temperatures, the heater being so constructed that maximum heatis generated only inthose parts immersed I in the liquid and the dangerof structural failure of the heater parts will be substantiallyminimized. A still further object is an improved method of heating aliquid utilizing the improved heater of this invention. These andfurther objects will be apparent from the following description of theinvention.

The above objects may be accomplished in accordance with my invention bypartially burning a gaseous or liquid fuel in an upper chamber, passingthe partially burned gases to a lower vertical shell immersed in theliquid being heated, and supplying sufiicient air to the partiallyburned gases in the lower shell so as to complete the combustion anddevelop maximum heat ina zone 2 within the shell where maximum transferof heat to the liquid being heated occurs.

The invention will be better understood by reference to the attacheddrawing which is a vertical view, shown partly in section and partly inelevation, of one modification of the invention.

In the drawing, upper combustion chamber I, which is positionedhorizontally, has an inner lining of refractory material 2 and an outerprotective metal plate covering 3. Chamber I is provided with aninspection door 4, a clean-out door 5 and a burner 6 having a fuel inlet1 and an air inlet 8. Positioned below the forward portion of chamber Iis a vertical, cylindrical shell '9 whose lower end is closed. An innerconduit Ill functions to conduct the products of partial combustion fromthe forward end of chamber I to the lower-end of shell 9. Betweenconduit I0 and the walls of shell 9 is an intermediate tube II which isof substantially equal length with tube I0 and is annular with respectthereto. Conduit l9 and tube II together form an annular air chamber I2,since the bottom ends of those two members are closed off from theremaining space in shell 9 by circular member I3. Intermediate tube IIforms together with the walls of shell 9 a relatively narrow annularspace I4.

Tube I5 serves to deliver air to annular air chamber l2 and such air isadmitted to the stream of partially combusted gases as they flow throughthe burner by way of holes IS in the lower end of inner conduit I0.These holes are shown spaced around the circumference of inner tube II)in two rows. Annular space I4 adjacent the walls of shell 9 opens intostack II. The heater is shown partially immersed in a liquid bath I9provided with a cover I8 through which shell 9 passes. The heater issupported on cover I8 by means of flange 20 around shell 9. At'the pointat which tube I5 enters shell 9, there is provided a packing material 2|which may be an insulating cement or any other suitable material.

' In operation, a mixture of fuel and a deficiency of air is injectedfrom burner 6 into chamber I where partial combustion occurs. Theproducts of that partial combustion are delivered by inner conduit IIIto the bottom of shell 9. Suflicient air to complete combustion issupplied to the gas stream near the bottom of shell 9 through holes I6of conduit III by way of air chamber I2 and tube I5. Complete combustionoccurs at the bottom of shell 9 and in the annular space, I l

adjacent the side walls thereof. It will be noted that the portion ofthe heater wherein complete combustion occurs, i. e. that portion inwhich maximum heat is evolved, is the part which is immersed in theliquid being heated. The combustion gases pass from annular space [4into stack I1.

I have found that satisfactory operation of the heater described may beaccomplished by supplying sufiicient air with the fuel in the uppercombustion chamber to burn the fuel to the water and carbon monoxidestage. I prefer, when using fuel oil, to supply about 70% of the airrequired to support complete combustion along with the fuel to the uppercombustion chamber. That amount of air will cause the release of about60% of the heat value of fuel oil and will result in the gases passingfrom the upper combustion chamber having a temperature in the range ofaround 900-1000 C. About 30% of the air required for complete combustionis admitted to the gas stream by way of holes l6. Ihe temperatures ofthe gases in the zone where complete combustion occurs will, of course,vary depending upon the temperature of the liquid surrounding theimmersed part of the shell. With liquid being heated at a temperature inthe range of 8504300 C., I have operated the heater with temperatures inthe zone of complete combustion around 950-l000 C., or not more thanabout 100 C. higher than the temperature of the liquid surrounding theimmersed part of the heater. Without rapid transfer of heat to the bathbeing heated, the temperature in the zone of complete combustion would,of course, be much higher, e. g. in the range 1500-1600 C.

The distribution of the air required to complete combustion between theupper and lower zones of combustion may be varied considerably and willdepend largely upon the particular fuel being used. Generally, from 60to 70% of the air should be supplied with the fuel to the upper chamberwith the balance of the air being injected into the products of partialcombustion by way of holes I6 as described above. The quantity of air tobe supplied with the fuel to the upper chamber should be sufiicient toliberate from 55 to 65% of the total heat value of the fuel. Any fluidfuel, for example, any of the natural or artificial gaseous fuels, maybe used, but the invention is especially well suited for the use of fueloil.

I have found it very advantageous to supply the supplemental air from anannular chamber surrounding inner conduit 9 over its entire length, eventhough the injection of such air into the products of partial combustionis to be made only at the lower portion of the heater. This is becauseair supplied as indicated serves to cool inner tube l and alsointermediate tube ll and maintains those tubes at temperaturessufilciently low to prevent their failure. An additional advantage isthat air so delivered becomes thoroughly preheated before actualinjection.

As will be apparent from the foregoing description, the parts of theheater which are subjected to the greatest degree of heat are that partof shell 9 below the stack, the corresponding part of tube I l, and thelower part of inner conduit 1 0. The manner of burning and of supplyingsupplemental air operate to keep the temperatures of those parts as lowas possible. Thus, those parts of shell 9 which are subjected to thehighest temperatures are in direct contact with the bath being heatedwhich removes heat therefrom while the parts of the inner tubes of theheater subjected to the greater heat are cooled by means of .the streamof air in annular air chamber l2. The heater therefore is admirably wellconstructed for delivering large quantities of heat to a surroundingliquid medium while insuring maximum cooling of burner parts.

When using the heater for heating liquid baths at very hightemperatures, it will, of course, be desirable to construct the burnerparts of materials designed to withstand high temperatures, thus thevarious high temperature heat-resisting stainless steels may be used toconstruct those parts which cannot be advantageously lined withrefractory material. The choice of structural materials will, of course,depend upon the intended use of the heater and shell 9 should beconstructed of material which will be chemically resistant to theingredients of the bath being heated.

The immersion heater of my invention is particularly well-suited forheating liquid reaction mixtures wherein the production of cyanides iseffected. Such reactions require high temperatures and. an unusuallyhigh heat input as a result of which immersion heaters heretofore known,e. g. heaters of the U type, have not been satisfactory.

Various modifications may be made in the details of the heater. Forexample, the gaseous products of combustion may be withdrawn by way of aflue in the form of an annular passage around the vertical shell insteadof from one side .as illustrated in the drawing. Furthermore, the holesfor admitting air into the products of partial combustion need not bearranged in two rows as indicated but may be distributed around the endof the inner conduit in a variety of ways. It is important, however, forsatisfactory operation that such holes be in the lower end of the innertube If! so that maximum heat evolution will occur outside of tube E0 ina zone adjacent the walls of shell 9 where rapid transfer of heat to theSurrounding liquid bath results. Holes 16 are preferably spaced aroundtube H1 so that the jets of air delivered to the gas stream will opposeeach other. Positioning of the holes so that jets of air will impingedirectly upon the surface of tube 10 or shell 9 should be avoided.

Since many changes may be made in the details of the invention as setforth above without departing from the spirit and scope thereof, it isto be understood that the invention is not restricted to such detailsexcept as indicated in the appended claims.

I claim:

1. A heater of the type adapted for use by immersion in liquid to beheated which comprises an upper horizontal combustion chamber and alower vertical cylindrical shell having a closed lower end adapted to beimmersed in the liquid being heated, a cylindrical concentric conduitWithin said shell adapted to lead products of partial combustion fromthe forward end of said upper chamber to the bottom of said shell, thewalls of said conduit being provided near its lower end with a pluralityof holes spaced around .said walls, an annular member between said shelland said conduit, said annular member being of substantially the samelength as said conduit and forming therewith an annular airchamberwithin said shell, means for delivering air into the upperportion of said air chamber, and means for exhausting combustion gasesfrom the upper portion of said shell.

2. A heater of the type adapted for use by iminersion in a liquid to beheated which comprises an upper horizontal combustion chamber and alower vertical cylindrical shell having a closed lower end and adaptedto be immersed in the liquid being heated, two concentric cylindricalconduits of substantially equal length positioned 5 within said shell soas to provide an annular air chamber within said shell, the inner-mostof said conduits being adapted to lead products of partial combustionfrom the forward end of said upper chamber to the bottom of said shell,the walls of the lower portion of said inner-most conduit being providedwith a plurality of holes spaced around said walls, the outer-most ofsaid conduits forming with said shell an annular space leading to astack and a tube for supplying air 15 to said annular air chamber.

FRANK E. SMITH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,923,614 Clarkson Aug. 22, 19332,059,523 Hepburn et a1. Nov. 3, 1936 2,118,479 See et al. May 24, 193810 2,200,731 Woodson May 14, 1940 FOREIGN PATENTS Number Country Date502,112 Great Britain Mar. 13, 1939

